Active agents (or drugs) are most conventionally administered either orally or by injection. Unfortunately, many agents are completely ineffective or have radically reduced efficacy when orally administered since they either are not absorbed or are adversely affected before entering the bloodstream and thus do not possess the desired activity. Further, orally administered agents typically do not take effect as quickly as injected agents. On the other hand, the direct injection of the agent into the bloodstream, while assuring no modification of the agent during administration, is a difficult, inconvenient, painful and uncomfortable procedure which sometimes results in poor patient compliance.
Hence, in principle, transdermal delivery provides for a method of administering active agents that would otherwise need to be delivered via hypodermic injection or intravenous infusion. Transdermal agent delivery offers improvements in both of these areas. Transdermal delivery, when compared to oral delivery, avoids the harsh environment of the digestive tract, bypasses gastrointestinal drug metabolism, reduces first-pass effects and avoids the possible deactivation by digestive and liver enzymes.
The word “transdermal”, as used herein, refers to delivery of an active agent (e.g., a therapeutic agent, such as a drug or an immunologically active agent, such as a vaccine) through the skin to the local tissue or systemic circulatory system without substantial cutting or penetration of the skin, such as cutting with a surgical knife or piercing the skin with a hypodermic needle.
Transdermal agent delivery systems generally rely on passive diffusion to administer the agent, while active transdermal agent delivery systems rely on an external energy source, including electricity (e.g., iontophoresis) and ultrasound (e.g., phonophoresis), to deliver the agent. Passive transdermal agent delivery systems, which are more common, typically include an agent reservoir containing a high concentration of the agent. The reservoir is adapted to contact the skin, which enables the agent to diffuse through the skin and into the body tissues or bloodstream of a patient.
As is well known in the art, transdermal agent flux is dependent upon the condition of the skin, the size and physical/chemical properties of the agent molecule, and the concentration gradient across the skin. Because of the low permeability of the skin to many active agents, transdermal delivery has had limited applications. This low permeability is attributed primarily to the stratum corneum, the outermost skin layer, which consists of flat, dead cells filled with keratin fibers (i.e., keratinocytes) surrounded by lipid bilayers. This highly-ordered structure of the lipid bilayers confers a relatively impermeable character to the stratum corneum.
One common method of increasing the passive transdermal diffusional agent flux involves pre-treating the skin with, or co-delivering with the drug, a skin permeation enhancer. A permeation enhancer, when applied to a body surface through which the agent is delivered, enhances the flux of the agent therethrough. However, the efficacy of these methods in enhancing transdermal protein flux has, in several instances, been limited.
As stated, active transport systems use an external energy source to assist and, in most instances, enhance agent flux through the stratum corneum. One such enhancement for transdermal agent delivery is referred to as “electrotransport.” Electrotransport uses an electrical potential, which results in the application of electric current to aid in the transport of the agent through a body surface, such as skin.
There also have been many techniques and systems developed to mechanically penetrate or disrupt the outermost skin layers thereby creating pathways into the skin in order to enhance the amount of agent being transdermally delivered. Early vaccination devices, known as scarifiers, generally included a plurality of tines or needles that were applied to the skin to and scratch or make small cuts in the area of application. The vaccine was applied either topically on the skin, such as disclosed in U.S. Pat. No. 5,487,726, or as a wetted liquid applied to the scarifier tines, such as disclosed in U.S. Pat. Nos. 4,453,926, 4,109,655, and 3,136,314.
There are, however, numerous disadvantages and drawbacks associated with scarifiers. A serious disadvantage in using a scarifier to deliver an agent is the difficulty in determining the transdermal agent flux and the resulting dosage delivered. Also, due to the elastic, deforming and resilient nature of skin to deflect and resist puncturing, the tiny piercing elements often do not uniformly penetrate the skin and/or are wiped free of a liquid coating of an agent upon skin penetration.
Additionally, due to the self-healing process of the skin, the punctures or slits made in the skin tend to close up after removal of the piercing elements from the stratum corneum. Thus, the elastic nature of the skin acts to remove the active agent liquid coating that has been applied to the tiny piercing elements upon penetration of these elements into the skin. Furthermore, the tiny slits formed by the piercing elements heal quickly after removal of the device, thus limiting the passage of the liquid agent solution through the passageways created by the piercing elements and in turn limiting the transdermal flux of such devices.
Other systems and apparatus that employ tiny skin piercing elements to enhance transdermal drug delivery are disclosed in U.S. Pat. Nos. 5,879,326, 3,814,097, 5,279,54, 5,250,023, 3,964,482, Reissue No. 25,637, and PCT Publication Nos. WO 96/37155, WO 96/37256, WO 96/17648, WO 97/03718, WO 98/11937, WO 98/00193, WO 97/48440, WO 97/48441, WO 97/48442, WO 98/00193, WO 99/64580, WO 98/28037, WO 98/29298, and WO 98/29365; all incorporated herein by reference in their entirety.
The disclosed systems and apparatus employ piercing elements of various shapes, sizes and arrays to pierce the outermost layer (i.e., the stratum corneum) of the skin. The piercing elements disclosed in these references generally extend perpendicularly from a thin, flat member, such as a pad or sheet. The piercing elements in some of these devices are extremely small, some having a microprojection length of only about 25-400 microns and a microprojection thickness of only about 5-50 microns. These tiny piercing/cutting elements make correspondingly small microslits/microcuts in the stratum corneum for enhancing transdermal agent delivery therethrough.
The disclosed systems typically include a reservoir for holding the active agent and a delivery system that is adapted to transfer the agent from the reservoir through the stratum corneum, such as by hollow tines of the device itself. Illustrative is the device disclosed in PCT Pub. WO 93/17754, which has a liquid agent reservoir.
As disclosed in U.S. patent application Ser. No. 10/045,842, which is fully incorporated by reference herein, it is also possible to have the active agent that is to be delivered coated on the microprojections or microprojection array instead of contained in a physical reservoir. This eliminates the necessity of a separate physical reservoir and developing a agent formulation or composition specifically for the reservoir. The skin piercing microprotrusions have a dry coating of the pharmacologically active agent. Delivery of the agent is facilitated when the microprotrusions pierce the skin of a patient and the patient's interstitial fluid contacts and dissolves the active agent.
When microprojection arrays are used to improve delivery or sampling of agent through the skin, consistent, complete, and repeatable penetration is desired. Manual application of a skin patch, having microprojections protruding from its skin-contacting side, often results in significant variation in puncture depth across the length and width of the patch. In addition, manual application results in large variations in puncture depth between applications due to the manner in which the user applies the array a microprojection array to the stratum corneum with an automatic device, which provides in a consistent and repeatable manner, stratum corneum piercing, not only over the length and width of the microprotrusion array, but also from application of one microprojection array to the next.
Some known spring loaded applicator devices for delivery of lancets for body fluid (e.g., blood) sampling are described in PCT Pub. No. WO 99/26539 and WO 97/42886. However, these devices are difficult to use because they require two-handed pre-setting of the applicator device prior to the application. In particular, the known spring loaded lancet applicators require either two sections of the device to be pulled apart for pre-setting or require one part of the device to be pulled apart for pre-setting or require one part of the device to be twisted with respect to another part of the device for pre-setting. In both of these motions, a two-handed pre-setting operation is required. Many of the patients using these devices possess neither the strength, nor the manual dexterity to pre-set these known applicator devices.
In U.S. application Ser. No. 09/976,763 a further spring loaded applicator, which is adapted to apply a microprojection array, is disclosed. The noted applicator includes a pre-setting mechanism that allows one-handed pre-setting of the applicator.
A drawback of the applicator is thus that the applicator still requires a separate step of manually pre-setting the device prior to use. It would thus be desirable to provide an applicator that is eliminates the step of manually pre-setting the applicator prior to use.
It is therefore an object of the present invention to provide an applicator for applying a microprojection member or array to a patient that substantially reduces or eliminates the aforementioned drawbacks and disadvantages associated with prior art applicator devices.
It is another object of the present invention to provide an auto pre-setting applicator that eliminates the step of manually pre-setting the applicator prior to use.
It is another object of the present invention to provide an auto pre-setting and auto triggering applicator that is adapted to apply a microprojection member or array to a patient.
It is another object of the present invention to provide an auto pre-setting and auto triggering applicator that applies microprojection arrays in a consistent and repeatable manner.
It is another object of the present invention to provide an auto pre-setting and auto triggering for applying a microprojection array that is compact in design.
It is another object of the present invention to provide an auto pre-setting and auto triggering applicator for applying a microprojection array that requires minimal components and has an extended useful life.